Interface ObjectFactory

The JNDI framework allows for object implementations to
be loaded in dynamically via object factories.
For example, when looking up a printer bound in the name space,
if the print service binds printer names to References, the printer
Reference could be used to create a printer object, so that
the caller of lookup can directly operate on the printer object
after the lookup.

An ObjectFactory is responsible
for creating objects of a specific type. In the above example,
you may have a PrinterObjectFactory for creating Printer objects.

An object factory must implement the ObjectFactory interface.
In addition, the factory class must be public and must have a
public constructor that accepts no parameters.

The getObjectInstance() method of an object factory may
be invoked multiple times, possibly using different parameters.
The implementation is thread-safe.

The mention of URL in the documentation for this class refers to
a URL string as defined by RFC 1738 and its related RFCs. It is
any string that conforms to the syntax described therein, and
may not always have corresponding support in the java.net.URL
class or Web browsers.

Method Detail

getObjectInstance

Creates an object using the location or reference information
specified.

Special requirements of this object are supplied
using environment.
An example of such an environment property is user identity
information.

NamingManager.getObjectInstance()
successively loads in object factories and invokes this method
on them until one produces a non-null answer. When an exception
is thrown by an object factory, the exception is passed on to the caller
of NamingManager.getObjectInstance()
(and no search is made for other factories
that may produce a non-null answer).
An object factory should only throw an exception if it is sure that
it is the only intended factory and that no other object factories
should be tried.
If this factory cannot create an object using the arguments supplied,
it should return null.

A URL context factory is a special ObjectFactory that
creates contexts for resolving URLs or objects whose locations
are specified by URLs. The getObjectInstance() method
of a URL context factory will obey the following rules.

If obj is null, create a context for resolving URLs of the
scheme associated with this factory. The resulting context is not tied
to a specific URL: it is able to handle arbitrary URLs with this factory's
scheme id. For example, invoking getObjectInstance() with
obj set to null on an LDAP URL context factory would return a
context that can resolve LDAP URLs
such as "ldap://ldap.wiz.com/o=wiz,c=us" and
"ldap://ldap.umich.edu/o=umich,c=us".

If obj is a URL string, create an object (typically a context)
identified by the URL. For example, suppose this is an LDAP URL context
factory. If obj is "ldap://ldap.wiz.com/o=wiz,c=us",
getObjectInstance() would return the context named by the distinguished
name "o=wiz, c=us" at the LDAP server ldap.wiz.com. This context can
then be used to resolve LDAP names (such as "cn=George")
relative to that context.

If obj is an array of URL strings, the assumption is that the
URLs are equivalent in terms of the context to which they refer.
Verification of whether the URLs are, or need to be, equivalent is up
to the context factory. The order of the URLs in the array is
not significant.
The object returned by getObjectInstance() is like that of the single
URL case. It is the object named by the URLs.

If obj is of any other type, the behavior of
getObjectInstance() is determined by the context factory
implementation.

The name and environment parameters
are owned by the caller.
The implementation will not modify these objects or keep references
to them, although it may keep references to clones or copies.

Name and Context Parameters.
The name and nameCtx parameters may
optionally be used to specify the name of the object being created.
name is the name of the object, relative to context
nameCtx.
If there are several possible contexts from which the object
could be named -- as will often be the case -- it is up to
the caller to select one. A good rule of thumb is to select the
"deepest" context available.
If nameCtx is null, name is relative
to the default initial context. If no name is being specified, the
name parameter should be null.
If a factory uses nameCtx it should synchronize its use
against concurrent access, since context implementations are not
guaranteed to be thread-safe.

Parameters:

obj - The possibly null object containing location or reference
information that can be used in creating an object.

name - The name of this object relative to nameCtx,
or null if no name is specified.

nameCtx - The context relative to which the name
parameter is specified, or null if name is
relative to the default initial context.

environment - The possibly null environment that is used in
creating the object.

Returns:

The object created; null if an object cannot be created.

Throws:

Exception - if this object factory encountered an exception
while attempting to create an object, and no other object factories are
to be tried.